The present invention relates generally to an anti-knocking control system, more particularly to a system for detecting knock-occuring conditions of an internal combustion engine and thereby controlling the internal combustion engine to prevent the occurrence of knocking in accordance with the results of detection of the knock-occuring conditions.
Generally, an anti-knock control system for use in an internal combustion engine is known as a means for optimally controlling the ignition timing of the engine in accordance with an output signal of a knock sensor sensing the vibrations of the engine with a view to improving the output of the engine concurrently with fuel consumption. An important problem in anti-knock controlling art relates to the need for a knock sensor which provides an accurate detection of engine knocking conditions.
In order to meet the requirements for manufacturing cost and reliability there is currently employed a knock sensor of the type wherein the detection is made with respect to the vibrations of an internal combustion engine. Such a knock sensor would suffer from deterioration of signal-to-noise ratio (S/N ratio) due to the occurrence of mechanical engine vibrations resulting from a high speed operation of the engine, resulting in difficulty of a precise knock detection upon a high speed travelling of a motor vehicle. One known approach to resolution of the affection of mechanical engine vibrations under the high speed operating conditions of the engine is to use knock sensors arranged to sense the knocking of the engine on the basis of the pressure variations or the combustion light in engine cylinders.
However, these prior knock sensors do not still produce satisfactory results for meeting the requirements in terms of accurate detections of engine knock, because it is impossible for these knock sensors, for example, to resolve the problems arising in connection with the variations of output characteristics of the knock sensors owing to secular change and fabrication tolerance and the variations of vibration transfer characteristics of engines due to passage of time and engine equation.
Therefore, attempts to avoid the problems noted above have been hitherto, the techniques being disclosed in U.S. patent application Ser. No. 735,108, filed on May 17, 1985, now U.S. Pat. No. 4,617,895, and U.S. patent application Ser. No. 891,165, filed on July 31, 1986, both assigned to the assignee of this patent application. Such techniques involve determining the presence of engine knocking in accordance with the pattern of a distribution of logarithmic transformation values of the maximum values or predetermined magnitude values of signals obtained from a knock sensor within a predetermined interval. However, a further improvement would be required from the viewpoint of reliability in detection of knocking condition and anti-knocking control and simplification in construction.